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Software helps size, select motors

Software can help engineers select the right motor regardless of application and be useful for new and seasoned engineers alike. But understanding how the facility’s environment will affect motion system requirements remains crucial in selecting the right motor.

Matt Prellwitz
02/06/2017

Figure 1: Even if the user doesn’t know all the application details, there are built-in tools to help calculate numbers for some variables that may be harder to track down such as inertia. Courtesy: Beckhoff AutomationApplication requirements dictate motor types when engineers define motion system specifications. Software also can help engineers pick the right motor regardless of application and such systems, along with a clear understanding of how the facility's environment will affect motion system requirements-are crucial in selecting the right motor. But they must also consider numerous factors, such as available space, power type, voltage and amperage, and the existing system, to accommodate the new motion system.

Most motor vendors will provide a large number of options from their product catalog and can specify the best motor for the application, which saves time. However, not every application is alike. Many automation providers have created feature-filled software that can assist in choosing the best available device for every application. These systems generally require only a few variables such as torque and required operating speeds to be entered before they calculate the correct motor and related equipment for the job.

Sizing software—also referred to as motion design software—starts with the user building their mechanical system and entering the relevant data into the system. Once all the required specifics about the application have been entered, the tool will calculate necessary motor specs and recommend a device. 

Motor details

Even if the user doesn't know all the application details, there are built-in tools to help calculate numbers for some variables that may be harder to track down, such as inertia. After the mechanics are built, motion profiles are needed. These will help with drive and motor selection, and determine if a gearbox is needed to keep the inertia ratio within the application's recommended tolerance.

General motor knowledge will help the user choose the right device for the task. For example, knowing that three-phase power will yield more speed in an application than single-phase—or that higher amperage will allow more torque—goes a long way in narrowing down choices when faced with a large number of motor options. 

Motion system inertia effect

Inertia is another factor that is often overlooked, but is really important when it comes to commissioning the motion system. Having an inertia of 1:3 or 1:5 accelerates the tuning process during the commissioning phase. Higher inertia ratios are being realized as faster control loops and higher-level utilities become easier to understand thanks to tools such as Bode Plots and 5th order velocity observer. This facilitates applications in the 10:1 to 30:1 ratios. Capable motion design software allows much of the math to be calculated automatically, which spares the users potential computational headaches.

After the motor and drive system have been selected, working with a vendor that supports commonly recognized, open standards for motion commands makes programming less complicated. Leveraging a drive system and software platform that allows the user to switch between one or two encoders for one axis can help with overall mechanical accuracy. A high-speed, real-time Fieldbus also enables responsive control without the need to configure hubs or switches for motion interruptions to update velocity for multiple axes simultaneously.

Figure 2: After the mechanics are built, motion profiles are needed, which will help with drive and motor selection and will determine if a gearbox is needed to keep the inertia ratio within the application’s recommended tolerance. Courtesy: Beckhoff Auto

Doing the requisite homework on motion requirements for an application and limiting complication factors within the plant will lead users down the best path. Choosing a robust motion design software platform will streamline the design phase and help engineers select the best available options for their machines and plants.

Matt Prellwitz, drive technology application specialist, Beckhoff Automation. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, cvavra(at)cfemedia.com.

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